Power supply devices of this type are generally known.
The cut-off frequency is that frequency which the field effect transistor can still just switch. The freewheeling diode is not taken into account in the context of determining the cut-off frequency. The cut-off frequency is an intrinsic property of the field effect transistor. The recovery time of the freewheeling diode is that time which elapses after the turn-off of a voltage directed in the forward direction to the freewheeling diode until the blocking effect of the diode is established again. The recovery time is an intrinsic property of the freewheeling diode.
In conventional power supply devices, a MOSFET is typically used as field effect transistor. In the case of a plurality of MOSFETs connected in parallel, in addition a high-frequency combiner is furthermore required.
Conventional MOSFETs have an intrinsic body diode as freewheeling diode, that is to say a diode integrated into the respective MOSFET. Said intrinsic body diode generally has a relatively long recovery time. The time is generally considerably greater than the reciprocal of the cut-off frequency of the MOSFET. In conventional devices, therefore, care has to be taken to ensure that the operating frequency of the field effect transistor remains low enough that its reciprocal is above the recovery time of the freewheeling diode. Alternatively or additionally, a corresponding matching circuit (for example a so-called circulator) has to be used to ensure that reflection of power back to the switching stages is avoided. Otherwise, the switching stage would be destroyed.
In the case where a plurality of switching stages are connected in parallel, the design of the matching circuit turns out to be extremely complex. This holds true especially in the case of pulsed operation of the load, during which reflections have to be avoided in a wide frequency spectrum. In such a case, the power supply device overall turns out to be correspondingly complex and expensive.